Rotor assemblies for relatively high speed heavy machinery such as hammer mills and wood hogs for fragmenting waste wood such as demolition debris, stumps, pallets, large timbers, and the like into particulate or chips, which are useful, are known. The present assignee owns U.S. Pat. No. 5,713,525 issued Feb. 3, 1998 for a typical wood hog machine and U.S. Pat. No. 5,419,502 issued May 30, 1995 for a typical tub grinder hammer mill system. Machines of this character are well classified as heavy machinery which require considerable driving power. Such machinery includes typically a multiplicity of hammers with hammer heads, mounting hammer knives on their rotatable outer ends.